Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes. For the latter application, a drill string is typically used in which a plurality of rods are coupled end-to-end via threaded joints as the depth of the hole increases. A terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes. WO 2006/033606 discloses a typically drill bit comprising a drill head that mounts a plurality of hard cutting inserts, commonly referred to as buttons. Such buttons comprise a carbide based material to enhance the lifetime of the drill bit.
Fluid is typically flushed through the drill string and exits at the base of the borehole via apertures in the drill head to flush the rock cuttings from the boring region to be conveyed backward and through the bore around the outside of the drill string. Further examples of percussive drill bits are disclosed in DE 3519592; U.S. Pat. No. 3,388,756; GB 692,373; RU 2019674; US 2002/0153174; U.S. Pat. No. 3,357,507, US 2008/0087473; WO 2009/067073 and WO 2013/068262.
Typically, a plurality of flushing grooves are recessed in the drill head to allow the fractured material to be transported rearwardly from the drill bit via the flushing fluid. U.S. Pat. No. 5,794,728 discloses a percussion rock drill bit having a plurality of fluid passageways that extend from a central bore of the bit to emerge at flushing grooves at the front face. However conventional bits are disadvantageous for a number of reasons. In particular, conventional flushing grooves are not optimised to facilitate fluid flow axially rearward from the front face and this reduces accordingly the drilling performance and in particular the penetration rate of the bit. Additionally, it is not uncommon for the axially forwardmost part of the flushing fluid passageway to become damaged due to contact with the rock that in turn decreases the delivery of fluid to the front face and also the efficiency of rearward flushing of fines and debris material cut from the rock face. Accordingly, what is required is a drill bit that addresses the above problems.